Biodegradable polymers are now attracting considerable attention, due to their peculiar characteristics related to degradability, in various fields of industry such as medical, agricultural and environmental fields and being considered to be of a great value particularly in the medical and environmental fields.
Biodegradable polymers are largely classified into natural biodegradable polymers and synthetic biodegradable polymers. Natural biodegradable polymers synthesized from naturally occurring substances are very environment-friendly and excellent in physical performance and biological adaptability. But the natural biodegradable polymers are very expensive and uncontrollable in regard to properties, since they are originated from natural substances.
On the other hand, synthetic biodegradable polymers are recently considered to be of a great commercial value because they are controllable in properties, unlike natural biodegradable polymers.
Among the synthetic biodegradable polymers, polyglycolide (PGA) and polylactide (PLA) are particularly excellent in performance and applied for various uses in the medical field due to their environment-friendliness and innoxiousness to living bodies. For example, they have been developed and used for DDS (Drug Delivery System), bone- or tissue-fixing pins, screws or stitching fibers, and so forth.
But the solid process of these polymers may result in non-uniformity of properties, deterioration of workability. Particularly, the polymers prepared in the massive solid state are to be grinded in proper size prior to a forming process, and the polymer grinding step is difficult to perform in the case of mass production on a commercial scale.
For some uses, such as DDS, the polymers are to be controllable in the type and size of particles for the sake of controlling the release rate of drugs. To solve this problem, many studies have been made on the preparation methods for minutely controlling the dissolution-extraction process of the polymer using solvent and non-solvent conditions, for example, by SAS (Supercritical Anti-Solvent) method. But these preparation methods are incomplete in that the polymer is uncontrollable in molecular weight and particle size and the production yield is extremely low.